WASHINGTON (Reuters) – President Barack Obamaâ€™s drawdown in Afghanistan will begin slowly, with the departure of just 800 National Guard troops this summer, followed by some 800 Marines in the fall, U.S. officials said on Wednesday.

The details provided by Lieutenant General David Rodriguez, the outgoing No. 2 commander of U.S. forces in Afghanistan, and Pentagon officials offered the most detailed look so far at how the U.S. military intends to carry out the withdrawal ordered by Obama in June.

Facing growing political opposition to the nearly decade-old war, Obama announced plans to pull out about a third of the 100,000 U.S. forces in Afghanistan by the end of summer 2012 — a faster timetable than the military had recommended.

The first 10,000 troops will come home by the end of the year. But Obama left the details up to his commanders.

â€œWe have begun the process of working ourselves out of a job — meaning we will hand over the lead to the Afghans gradually, over time,â€ said Rodriguez, speaking to reporters in a video-conference from Afghanistan.

The Pentagonâ€™s small initial drawdown leaves as many as 8,400 troops to withdraw in the last few months of 2011, and Rodriguez said he expected commanders to wait until later in the fall before deciding how to thin out those forces.

Jeffrey Dressler at the Institute for the Study of War, a Washington D.C.-based think tank, said Rodriguezâ€™s announcement was within expectations — particularly given the need to keep the bulk of troops in place until the end of the year.

â€œWhat the commanders are trying to do is conserve as much combat power as they can until the end of the fighting season,â€ Dressler said.

Rodriguez and the Pentagon offered the following details on the initial drawdown, without ruling out further changes.

* The Army National Guardâ€™s 1st Squadron, 134th Cavalry Regiment in Kabul, with about 300 troops, leaves in July.

* The Army National Guardâ€™s 1st Squadron, 113rd Cavalry Regiment, also leaves in July.

Critics have said Obamaâ€™s decision to bring troops home from Afghanistan faster than the military has recommended could jeopardize the next major push of the war, to unseat insurgents in the east. Republican Senator John McCain, speaking in Kabul on Sunday, said Obamaâ€™s drawdown plan created â€œunnecessary risk.â€

Although extra U.S. troops ordered into southern Afghanistan have made security gains there, the situation in the east of the country bordering Pakistan has deteriorated.

Rodriguez, however, said U.S. military plans to shift the focus to the east remained on track, despite the drawdown.

â€œAs we continue to maintain the momentum in the south … we will end up thinning out down there first, and then focusing more and more of our energy in the east,â€ he said.

Still, he declined to say when that might happen, adding: â€œItâ€™s a little bit too early to take that guess right now.â€

The drawdown comes amid intense fighting in Afghanistan, where more than 1,500 U.S. forces have been killed since the war began. Last week, insurgents staged a brazen raid on the Kabul Intercontinental hotel, killing 12 people and raising fresh questions about whether Afghan forces are ready to assume responsibilities as U.S. forces pull out.

Rodriguez commended the Afghan forces on what he called a â€œgreat responseâ€ to the attack but played down expectations that violence would ebb any time soon.

Asked whether he expected violence to start subsiding this year or next, Rodriguez said: â€œThat remains to be seen. Itâ€™ll actually probably be next year.â€